When processing a substrate (wafer) in a semiconductor manufacturing process in a vacuum, a temperature control operation for making the surface temperature of the substrate uniform has been performed to enhance processing uniformity. As a substrate temperature control means, a temperature control operation may be performed by forming a coolant flow path within a substrate stage for mounting a substrate. Coolant may be allowed to flow through the flow path thereby cooling the surface of the substrate mounted on the substrate stage with radiant heat radiating from the substrate stage.
For example, JP9-17770A discloses a plasma processing apparatus in which two concentric coolant flow paths are formed within a substrate stage. The temperature of the coolant flowing through the outer flow path differs from that of the coolant flowing through the inner flow path. Thus, the peripheral portion of a substrate exposed to radiant heat radiating from the inner wall of a chamber is cooled more heavily than the central portion of the substrate, thereby attempting to keep the surface temperature of the substrate uniform.
In the plasma processing apparatus disclosed in JP9-17770A, however, the two coolant flow paths, through which coolants differing in temperature flow, are arranged adjacent to each other within one substrate stage. Thus, the temperatures of the two coolant flow paths affect each other, and there is a concern that the cooling operations of the central portion and the peripheral portion of the substrate cannot be independently controlled. In other words, it becomes impossible to precisely manage and control the temperatures of the central portion and the peripheral portion of the substrate mounted on the substrate stage. This makes it difficult to make the surface temperature of the substrate uniform because the surface temperature of the peripheral portion of the substrate is greatly influenced by the radiant heat radiating from the inner wall of a chamber and the surface temperature of the central portion of the substrate is less affected by the radiant heat. Thus, since the entire surface of the substrate is not kept at a uniform temperature when processing the substrate, the substrate cannot be processed uniformly. Moreover, the integral formation of the substrate stage within the plasma processing apparatus is also the reason why the temperatures of the two coolant flow paths have an influence on each other and the temperatures of the central portion and the peripheral portion of the substrate cannot be independently controlled.